This invention relates to an air cleaning apparatus. A conventional air cleaning apparatus disclosed, for example, in Japanese Pat. No. 996,051 is known. More particularly, a conventional air cleaner has, as shown in FIG. 1, a plurality of dust collecting electrodes 1 formed of aluminum, corresponding electrodes 2 alternately arranged between dust collecting electrodes 1 at intervals of approx. 10 mm to form air flow passages, and ionizing wires 3 installed outside of the electrodes at a distance r from the line connecting the ends of the respective electrodes 1 on extension lines extended from the respective electrodes 2. The distance r is approx. 20 mm. The wires 3 and each electrode 2 are commonly connected as positive polarity, the electrodes 1 being of negative polarity, and a voltage of approx. 15 kV is applied from a power source 4 between the electrodes and the wires. A corona discharge is produced between each wire 3 and the respective electrode 1 upon application of the voltage therebetween, thereby charging kinetic energy to neutral gas molecules to generate an air stream directed from the wires 3 toward the interval between the respective electrodes when ions are moved to the side of the electrodes 1. Further, when the air stream is produced, fine particles in the air charged in ions are collected on the dust collecting electrodes 1. Moreover, remaining fine particles which have not been completely collected are collected on the electrodes 1 by means of an electric field formed between the electrodes 2 and 1 in the course of the air flowing in the interval. In case that the voltage supplied from the power source 4 has a constant value, the force for producing an air stream in parallel with the panel surface of the electrodes 1 in the interval is, as shown in FIG. 1, given by the component force F cos .theta. of the force F directed from the wire 3 to the electrode 1, where .theta. is an opening angle from the wire 3 as an origin between the end of the electrode 1 and the end of the electrode 2. When the distance r has reached 0 in this case, the angle .theta. approaches 90.degree. and accordingly the force F cos .theta. approaches 0. Thus, the force for producing the air stream is almost vanished. When the distance r is, on the other hand, increased, a magnetic field between the end of the wire 3 and the end of the electrode 1 decreases proportionally to 1/r.sup.2, thereby remarkably weakening the corona discharge electric field. Thus, similarly to the above, the air stream almost stops. Accordingly, when the power source voltage is constant, an adequate value exists in the set range of the distance r, thereby defining the velocity of the air stream to be produced substantially to a predetermined value.
However, in such a conventional air cleaner, the dust collecting efficiency is insufficient in practical use due to the long interval of approx. 10 mm between the dust collecting electrode and the corresponding electrode. In addition, since no means is provided against a zone generated by corona discharge, the zone flow rate out of the air cleaner can amount to approx. 200 ppb, which may influence a human body.
The volume and the cleaning efficiency of a chamber to be cleaned by an air cleaner are different depending upon the purpose of using the chamber. Thus, the air cleaner requires the corresponding performance. However, in the conventional air cleaner, the velocity of the air stream to be produced is defined substantially by a predetermined value when the voltage of the power source is defined by a constant value. Therefore, the conventional air cleaner has drawbacks and does not sufficiently meet the above-described requirements.